Author Topic: dubcats secret little hideout  (Read 129766 times)

2018-01-26, 01:54:00
Reply #120

Dionysios.TS

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2018-01-26, 15:24:48
Reply #121

Fluss

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Dubcat I don't understand what you're trying to demonstrate in your last post. Can you explain a little bit further pls?

2018-01-26, 15:43:34
Reply #122

romullus

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Open images in new tabs and switch between them. Look at sphere's shadow terminator - the difference should be obvious.
I'm not Corona Team member. Everything i say, is my personal opinion only.
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2018-01-27, 17:22:25
Reply #123

dubcat

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Can you explain a little bit further pls?

As romullus said :)

--------------------------------------------------------------

I'm posting a little weekend present for you guys, these settings emulate the default ACES tonemapper with about 0.5 RGB error.
The settings might look ridiculous with negative "highlight compression", but trust me, give it a try ;)



I'm attaching a VFB settings file that you can load.
Remember to disable LUT if you are using one.

edit: I made these settings with "Corona 2018-01-25 Daily". I remember there were some filmic changes, but I can't remember if it was 1.6/1.7 or daily. Just letting you know in case stuff looks weird. The result should be pretty much identical to the ACES Photoshop script I posted earlier.
« Last Edit: 2018-01-28, 03:59:30 by dubcat »
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2018-01-28, 15:42:46
Reply #124

agentdark45

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I just tried out the above settings (with tweaked exposure) on some previous CXR's and I have to say I'm super impressed with the result!

Straight out of the VFB I'm getting some very pleasing images. Nice natural burnouts, good contrast/shadows and rich colours. We are definitely on to something here.

Comparison images below:

1. Default Corona settings with highlight compression at 8
2. Manually tweaked settings (no lut)
3. Manually tweaked settings (with lut)
4. Dubcat's settings
« Last Edit: 2018-01-28, 15:56:19 by agentdark45 »
Vray who?

2018-01-28, 21:31:23
Reply #125

Fluss

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Open images in new tabs and switch between them. Look at sphere's shadow terminator - the difference should be obvious.

Indeed, the transition between light and shadow is way softer in Fstorm. Much more pleasing to the eye.

How does the Vray alSurface shader does compare to this?

"The Fresnel effect is computed as part of the BRDF calculations (a.k.a. “glossy Fresnel”) and takes into account the viewing direction, the surface normal, and the light directions."

Isn't it related to this ?
nothing to do with the diffuse part, misread what you wrote

Also, As far as I remember, Corona shader does not support glossy fresnel.




What's more, some users are experiencing strange atifacts with SSS here :

https://corona-renderer.com/forum/index.php?topic=18702.0

Which seems to be the exact same issue descibed here :

Quote
VRay Skin Mtl: This uses a two lobe specular model with a sharp and broad reflection. It also uses Phong as the reflective BRDF. This model proved to work well in many situations, but at glancing angles, based on the way that it would cut out the SSS, could cause darkening. This is because the Fresnel effect is computed as a function of the angle between the viewing direction and the surface normal, ignoring the directions from which lights illuminate the surfaces.

alSurface: This model also uses a two lobe specular model. However, instead of using a smooth BRDF like Phong or Blinn, it uses a microfacet one. The Fresnel effect is computed as part of the BRDF calculations (a.k.a. “glossy Fresnel”) and takes into account the viewing direction, the surface normal, and the light directions. The user has a choice between GGX and Beckmann BRDF models. Based on the nature of the micro faceting, it can avoid the darkening effect at the glancing angles through retro-reflection. Additionally it does not cover the SSS at the same glancing angles.

source : https://www.chaosgroup.com/blog/v-rays-implementation-of-the-anders-langlands-alsurface-shader

Of course, I might be totally misleading as i'm not a tech guru like some of you guys..

But there is one thing that bother me. We were experiencing some white halos on rough shaders some times ago. By looking at the examples here ( https://www.chaosgroup.com/blog/understanding-glossy-fresnel), it looks like a direct consequence of not supporting the glossy fresnel effect. It seems fixed now. But when i see that glossy fresnel isn't supported yet, i wonder if it has been fixed the correct way or with some workarounds (we have then seen some dark halos when the devs were trying to fix it, which strengthens me in my view that it wasn't done the right way).

Basically, initial implementation of the shader was good, it should be more reflective at grazing angles like it was doing BUT this effect should also be affected by the roughness as more micro-facets are facing the camera (so less grazing angles) on rough materials compared to shiny ones. If the whole thing is well implemented, angle affect should resolve by itself I guess.

fStorm split the HDRi into indirect and direct pass, and I think this is the reason fStorm has different shadow values.

That said, your statement totally make sense here.
« Last Edit: 2018-02-03, 16:48:51 by Fluss »

2018-01-29, 09:16:51
Reply #126

NicolasC

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Thanks A LOT Dubcat for all your investigations. Very instructive, a gold mine.
Hats off, really.
Nicolas Caplat

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2018-01-29, 17:05:05
Reply #127

Juraj Talcik

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Quote
it has been fixed the correct way or with some workarounds

It was some sort of workaround by manually fitting it to resemble the alsurface curve. And the diffuse part is still basic Lambert, which is responsible for the harsch look.

Ondra said he would like to look into this more now, not sure when that is but we should keep the pressure and push him towards it :- ).
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2018-01-31, 00:53:07
Reply #128

Dippndots

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Is your Megascans export script still available, Dubcat? The link in your Megascans thread 404s :(

2018-01-31, 10:15:48
Reply #129

Fluss

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Quote
it has been fixed the correct way or with some workarounds

It was some sort of workaround by manually fitting it to resemble the alsurface curve. And the diffuse part is still basic Lambert, which is responsible for the harsch look.

Ondra said he would like to look into this more now, not sure when that is but we should keep the pressure and push him towards it :- ).

Hopefully, corona 2.0 will bring Vray compatibility and OSL support so we might be able to try that alshader inside corona sooner than later.

2018-01-31, 10:29:55
Reply #130

Juraj Talcik

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OSL doesn't have access to BRDF though so I am not sure if we would get anything else than the values translated to CoronaMTL internally.
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2018-01-31, 11:25:22
Reply #131

Fluss

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OSL doesn't have access to BRDF though so I am not sure if we would get anything else than the values translated to CoronaMTL internally.

Just checked, you're right OSL does not allow to write custom BRDF / can only use what's available... That's sucks! So we have to wait for a proper 'state of the art' BSDF.

I was so optimistic ! Juraj you just ruined my day :)

2018-02-01, 09:04:18
Reply #132

Fluss

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dubcat, can you share your scene pls ? I'd like to make some direct comparison with Vray alshader.





2018-02-01, 16:43:24
Reply #133

dubcat

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We are definitely on to something here.

Glad you like it. :)

Thanks A LOT Dubcat

Thank you :)

Is your Megascans export script still available, Dubcat? The link in your Megascans thread 404s :(

I've been working on new scripts for Quixel since last winter.
The new scripts use my "Specular to IOR v2" LUT to auto convert specular maps, and they read the proper displacement height value from the json file.
I don't have a release date, but it will be worth the wait!

I'll make a new post here to inform you guys when it's released.

dubcat, can you share your scene pls ?

That scene is long gone, but I've made a new one for you. The zip contains a "Corona Sky" HDRi for consistent lighting and an fbx with geo/camera.
I had to use an external file sharing service, because the forum cap is at 30mb.

https://www.sharebase.net/58ed6f5e1e79212f



Hope I didn't miss any questions, if so, let me know.

edit:
I forgot to mention that Epic has fixed the blue light problem in Unreal.



edit edit:
Here is the ACES tonemapper if anyone is interested.

https://www.desmos.com/calculator/h8rbdpawxj

If you look at the numbers on the left side of each column, these are the parameters.

4   - Slope        - 0.88
7   - Toe           - 0.55
8   - Black Clip  - 0
11 - Shoulder   - 0.26
12 - White Clip - 0.04
« Last Edit: 2018-02-02, 03:47:00 by dubcat »
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2018-02-03, 12:45:55
Reply #134

Fluss

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Thanks dubcat for the scene. I'll make some comparison with shaders that support diffuse roughness
« Last Edit: 2018-02-03, 16:45:13 by Fluss »